In gas turbine engines, it is well known to connect turbine blades to turbine disks using “fir tree” connections. In such connections, each blade has a fir tree root which tapers inwardly in width with increasing inwards radial distance, the root being slidably insertable, along a substantially axial direction of the engine, into a respective conforming fir tree recess formed in the disk. The facing sides of the fir tree root and fir tree recess have respective interengaging serrations which take the form of projections and grooves extending in the direction of insertion of the root into the recess. In this way, the blades can be prevented from flying outwardly from the disk during operation of the engine.
It is also known to provide a space between the radially inward end of the blade root and the bottom of the recess so that cooling air, bled from the compressor, can be fed into the space, and from thence along interior channels in the blade, to cool the blade airfoil.
Although, such airfoil cooling can be effective, there still remains a problem of cooling the fir tree roots and the posts which extend radially from the disk to define the fir tree recesses therebetween.
To improve cooling in these regions, U.S. 2004/0191067 proposes truncating some of the fir tree projections to form cooling air flow paths extending from the front to the rear of the disk, and to supply such flow paths with cooling air bled from the compressor. In particular, U.S. 2004/0191067 proposes positioning a flange which covers the fir tree engaging features but is spaced therefrom so as to allow entry of cooling air via the space into the forward ends of the flow paths.